Staff EmeritusPremium

Yeah, that's the biggest problem. Messing with the tiers after your career has been started already can (and probably will) end in corrupting your saved game.

However, you could try to turn everything around after installing the mod. I.e. you swap ALL the performance data from Tier 1 with Tier 5, swap everything from Tier 2 to Tier 4 and so on. Basically, you'll need to make Tier 5 the worst but keep the top teams in there. That way your car will improve but well...the first one or two seasons will be harder. Just a weird idea, never tried that.